The invention is based on a priority application EP03291296.6 which is hereby incorporated by reference.
The present invention relates to a method for adjusting the relative output power of individual output wavelengths of a multi-output-wavelength Raman laser. Further, the present invention relates to a device that performs such a method, i.e. a device for adjusting the relative output power of individual output wavelengths of such a laser.
Multi-output-wavelength Raman lasers are per se known. These devices utilize the Raman effect for generating Laser output wavelengths in a wavelength range suitable for the amplification of communication signals propagating in optical fibers.
As is well known, the Raman effect relies on interaction of light with matter. Raman interaction is an inelastic scattering process in which incident pumplight is downshifted in frequency, thereby downshifted in photon energy by a certain amount that corresponds to excitation energies of certain vibrational modes of the matter. The light that has been downshifted in frequency is usually called Stokes light or simply Stokes.
In the case of solid state matter, the frequency of the scattered light may vary continuously as a function of a continuous vibrational spectrum of the solid state matter. The resulting broad and continuous spectrum of the scattered light is often called gain spectrum.
In particular, for a Ge-doped silica fiber, the maximum Raman gain for a “Stokes” corresponds to a frequency shift of 13,2 THz between the original pumplight and the maximum of the continuous gain spectrum. One Stokes is a general term for the downshifted light.
Multi-output-wavelength Raman lasers are utilized for pumping optical fibers. In an optical fiber, energy of the pump wave may be transferred to the signal that propagates along the fiber, by stimulated Raman scattering. Such an amplification requires the frequency of the optical signal to lie within the Raman gain spectrum of the pumplight. Hence, if amplification is desired for a wide range of signal frequencies, a respective broad spectrum is required, in which Raman gain occurs. Such a broad spectrum is achieved by pumping an optical fiber with a plurality of pump wavelengths that are chosen such that the gain spectra of these pump wavelengths overlap in order to result in the desired broad spectrum.
Multi-output-wavelength Raman lasers may, in general, provide for the needed plurality of pump wavelengths.
It is, however, necessary to adjust the optical power in each output wavelength of such a laser according to the needed configuration depending on the line fiber to pump.
Previously, the necessary adjustments rely on methods that have been individually developed for each individual multi-output-wavelength Raman laser.